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dbranch: fix handling of state-based acceptance

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Fixes issue #525.

* spot/twaalgos/dbranch.hh, NEWS: Document.
* spot/twaalgos/dbranch.cc: Detect cases where the acceptance should
be changed from state-based to transition-based.
* tests/python/dbranch.py: Add a test case.
This commit is contained in:
Alexandre Duret-Lutz 2023-02-03 09:35:46 +01:00
parent 5969aa4925
commit 058975c167
4 changed files with 59 additions and 8 deletions
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4
NEWS
View file

@ -18,6 +18,10 @@ New in spot 2.11.3.dev (not yet released)
incorrect handling of states without successors, causing some
segfaults. (Issue #524.)
- Running delay_branching_here() on state-based automata (this was not
done in Spot so far) may require the output to use transition-based
acceptance. (Issue #525.)
New in spot 2.11.3 (2022-12-09)
Bug fixes:

19
spot/twaalgos/dbranch.cc
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@ -66,6 +66,10 @@ namespace spot
hashmap_t first_dest[1 + is_game];
auto& g = aut->get_graph();
// Merging outgoing transitions may cause the automaton to need
// transition-based acceptance.
bool need_trans = !aut->prop_state_acc().is_true();
// setup a DFS
std::vector<bool> seen(ns);
std::stack<unsigned> todo;
@ -128,9 +132,18 @@ namespace spot
unsigned& mergedlast = g.state_storage(mergedst).succ_tail;
unsigned& candfirst = g.state_storage(canddst).succ;
if (mergedlast)
aut->edge_storage(mergedlast).next_succ = candfirst;
{
aut->edge_storage(mergedlast).next_succ = candfirst;
// Do we need to require transition-based acceptance?
if (!need_trans)
need_trans =
(aut->edge_storage(candfirst).acc
!= aut->edge_storage(mergedfirst).acc);
}
else // mergedst had no successor
mergedfirst = candfirst;
{
mergedfirst = candfirst;
}
mergedlast = candlast;
// 2) updating the source of the merged transitions
for (unsigned e2 = candfirst; e2 != 0;)
@ -149,6 +162,8 @@ namespace spot
changed = true;
}
}
if (need_trans)
aut->prop_state_acc(false);
return changed;
}
}

15
spot/twaalgos/dbranch.hh
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@ -1,5 +1,5 @@
// -*- coding: utf-8 -*-
// Copyright (C) 2022 Laboratoire de Recherche et Développement
// Copyright (C) 2022, 2023 Laboratoire de Recherche et Développement
// de l'Epita (LRDE).
//
// This file is part of Spot, a model checking library.
@ -26,10 +26,15 @@ namespace spot
/// \ingroup twa_algorithms
/// \brief Merge states to delay
///
/// If a state (x) has two outgoing transitions (x,l,m,y) and
/// (x,l,m,z) going to states (x) and (y) that have no other
/// incoming edges, then (y) and (z) can be merged (keeping the
/// union of their outgoing destinations).
/// In an automaton with transition-based acceptance, if a state (x)
/// has two outgoing transitions (x,l,m,y) and (x,l,m,z) going to
/// states (x) and (y) that have no other incoming edges, then (y)
/// and (z) can be merged (keeping the union of their outgoing
/// destinations).
///
/// If the input automaton uses state-based acceptance, running this
/// function might make the acceptance transition-based, but only if
/// two states with different acceptance are merged at some point.
///
/// \return true iff the automaton was modified.
SPOT_API bool delay_branching_here(const twa_graph_ptr& aut);

29
tests/python/dbranch.py
View file

@ -1,5 +1,5 @@
# -*- mode: python; coding: utf-8 -*-
# Copyright (C) 2022 Laboratoire de Recherche et
# Copyright (C) 2022, 2023 Laboratoire de Recherche et
# Développement de l'Epita (LRDE).
#
# This file is part of Spot, a model checking library.
@ -145,3 +145,30 @@ State: 5
State: 6
[t] 6
--END--""")
# Running delay_branching_here on state-based acceptance may require
# the output to use transition-based acceptance. (Issue #525.)
a = spot.automaton("""
HOA: v1 States: 4 Start: 0 AP: 2 "a" "b" Acceptance: 1 Inf(0) --BODY--
State: 0 [0] 1 [0] 2 State: 1 [1] 3 State: 2 {0} [!1] 3 State: 3 [t] 0
--END--""")
copy = spot.make_twa_graph(a, spot.twa_prop_set.all())
if spot.delay_branching_here(a):
a.purge_unreachable_states()
tc.assertTrue(spot.are_equivalent(a, copy))
tc.assertEqual(a.to_str(), """HOA: v1
States: 3
Start: 0
AP: 2 "b" "a"
acc-name: Buchi
Acceptance: 1 Inf(0)
properties: trans-labels explicit-labels trans-acc deterministic
--BODY--
State: 0
[1] 1
State: 1
[0] 2
[!0] 2 {0}
State: 2
[t] 0
--END--""")